DRAM drives for ZFS based systems and apps like High Frequency Trading

Assume that you are a storage systems integrator with two areas of focus:

High frequency Trading

High end NAS filers for enterprise use

Consider your first area of focus – High frequency trading (HFT). As we discussed before it is extremely fast trading by traders using supercharged computers, complex programs & algorithms and servers tactically co-located next to servers at a trading exchange. HFT traders capitalize on the split second advantages offered by their unique systems. If you are building computer infrastructure for high frequency trading then when it comes to memory devices that can handle transactional logging you have to choose between HDD, NAND flash based SSD and DRAM based SSDs.

For your second area of focus, you may be building high end NAS filers based on the Zettabyte File System and you will need an accelerator device for the ZFS Intent Log (ZIL). This accelerator device has to be optimized for synchronous writes and must exhibit two key characteristics:

Extremely low latency

Very high sustained write IOPS

In addition, The ZIL accelerator has to be accessible from both nodes of a 2 node cluster (for high availability) to allow both nodes to access the log. This precludes a single port SATA interface based NAND flash SSD and requires that you consider dual ported SAS SSDs. While traditional NAND flash based SAS SSD will give you an advantage over the fastest HDD, you are still dealing with SSDs which wear out over time. You are forced to decide between an eMLC NAND based SSD with 30,000 Program Erase (P/E) cycles or a relatively expensive SLC NAND based SSD with 200,000 P/E cycles.

Ideally you want a Non Volatile Memory (NVM) device with infinite endurance, ultra-low latency and extremely high sustained IOPS performance which stays consistent regardless of the IO distribution (random, sequential or mixed). Such a device would give you the best of both worlds: the SSD form factor that you are familiar with and the infinite endurance of DRAM. However DRAM based SSDs on the market today are more likely to exhibit latencies of ~23 micro seconds and ~65,000 read IOPS with 4K sustained and 50,000 write IOPS with 4K sustained. I would contend that you’d be better served with emerging products that exhibit ultra-low latencies of less than 5 micro seconds and 125,000 read IOPS with 4K sustained. When I think of how far these emerging DRAM drives have come in terms of performance, I’m reminded of the Oldsmobile jingle “This is not your father’s Oldsmobile”.

However if I leave you with the conclusion that these blazing fast DRAM drives are relevant only for HFT and ZFS ZIL then I would be doing you a dis-service. I believe that these emerging DRAM drives would be ideal devices to store log files for write-intensive mail systems, logs for Microsoft Exchange and metadata for file systems which allow you to separate metadata from file data.

So what do you think? Is a DRAM drive in your future? All constructive feedback from integrators and storage practitioners is welcome.